Connections between the hexon polypeptides in the two-dimensional hexon crystalline array.

Fine interhexonal connections were observed in high resolution electron micrographs of tight two-dimensional hexagonal crystalline arrays. Intrahexonal connections were found among the three polypeptides constituting the hexons. The length of the interhexonal connections was 2.73 mm, and their diameter 1.2 nm; that of the intrahexonal connections were 1.05 nm and 0.75 nm, respectively. The orientation of the hexons in a two-dimensional crystalline array corresponded to a corner to edge conjunction. One side of each of the three polypeptides, constituting a triangular hexon, corresponded to the sides of that hexon; their points of contact were the corners. A tentative diagram of the molecular arrangement of hexon polypeptides and of interhexonal connections was drawn up following analysis of the electron micrographs. It showed that parallel connections run to both ends of each polypeptide of a hexon, connected to one of the end parts of the two nearest polypeptides of the next hexon, as follows from the threefold symmetry. Thus, every hexon is joined to its six neighbours by six times two parallel connections. Two pairs of parallel connections enclose an angle of approximately 60 degrees.